The invention relates to the field of optical signal processing.
Amplitude encoded phase-only filters can be employed in Fourier transform optical correlators for determining whether a correlation exists between the Fourier transform of an input image and the transform of a reference image positioned within a spatial light modulator or filter at the Fourier transform plane. Such a correlation indicates a close match between the input image and the reference image. The present invention has been used in the classical VanderLugt filter at the Fourier transform plane and has several advantages over other methods such as the amplitude encoded phase-only filter for optical correlators disclosed in U.S. Pat. No. 5,024,508 to Horner and the averaged amplitude phase-only filter disclose in U.S. Pat. No. 5,148,316 to Horner and Flavin, both being incorporated by reference herein. First, the filter of the present invention is not restricted to positive values and thus no DC bias is required. Also, both the amplitude and binary phase of the filter can be economically implemented on a single spatial light modulator (SLM).